The present invention relates to a conveying device for conveying a tubing and a fluid medium contained in the tubing.
A device of this type finds application, for example, as part of an apparatus for internally coating flexible tubings. The device is used to convey the tubing in a direction along the longitudinal axis of the tubing, and also to convey a coating solution contained in the interior of the tubing in the direction of the tube movement. In so doing the device should ensure that the liquid level in the tubing is kept at a substantially constant level, keeping in mind that the quantity of coating solution used depends on the speed of the tubing.
German Auslegeschrift No. 25 57 994 describes a device, in which a tubing filled with coating solution is moved in the direction of its longitudinal axis at a constant speed, while at the same time liquid is transported upwardly in that portion of the tubing which is conveyed vertically upwardly. According to the document, by this measure the liquid level is kept at its initial height during the course of the process.
In this known device, a plurality of rotatable rollers are fastened to two roller stars, whereby each roller star rotates about its center point and at the same time traces a swinging motion in the direction of the tubing surface. Due to these various, superposed movements, it is technically very complicated to continuously achieve a precise adaptation of the circumferential speed of the rollers to the speed of the tubing, and additionally, to compensate for the slip which usually occurs on pressure rollers in the case of a spot contact. Therefore, from the control engineering point of view, driving the rollers is very complicated, if not entirely impossible. For proper operation, the roller speed has to correspond to the speed of the conveyed tubing minus the speed of the roller stars. The resulting motion is non-uniform and sine-shaped, and further depends on the quantity of liquid to be transported, which in turn depends on the diameter of the tubing employed.
Another device for performing such a process is described in German Auslegeschrift No. 26 59 000. This device comprises two conveyor belt-type endless belts with sine-shaped curvature on their outer surfaces. Firstly, the manufacture of these belts is technically very complicated. Additionally, these endless belts particularly have the disadvantage of undergoing non-uniform elongation during operation. Thus, the quantity of liquid conveyed can change undesirably. Moreover, adjusting the drive and mutually shifting the curvatures of the endless belts to achieve the exactness required is very difficult and susceptible to malfunction. Furthermore, there is the danger that the tubing may be damaged when engaged by two opposite bulgings of the endless belts. At the very least, the endless belts and the tubing are subject to severe wear and high mechanical stress due to their relative movement.
These same disadvantages are exhibited by the conveying and pumping device for internally coating tubings, which is disclosed in German Offenlegungsschrift No. 28 56 253. The device comprises a conveyor belt-type endless belt and a cylindrical roller, both of which are provided with profiled areas which are uniformly spaced around the entire circumference of the surfaces. In each of these devices, the liquid level is subject to strong fluctuations due to the fact that the liquid stream is delivered in a pulsating manner.
The device described in German Offenlegungsschrift No. 28 56 253 has been further developed into the device disclosed in German Utility Model No. 81 10 471, which evidences a non-profiled conveyor belt-type endless belt. Nevertheless, the mechanical stress exerted on the tubing by the action of the conveying means is still relatively high. Additionally, according to this device, the quantity of liquid which can be conveyed is restricted to the cavities formed by the bulgings. Moreover, an undesirable back flow of the liquid in the direction opposite the direction in which the tubing is moved cannot be excluded, since there is not a sufficiently pressure-tight seal between roller and belt. Furthermore, none of the aforementioned devices offers the possibility of conveying only the liquid contained in the tubing, while the tubing stands still, or, alternatively, of conveying only the tubing without conveying the liquid, or even of conveying the liquid in the direction opposite to the direction in which the tubing is moved. Additionally, it is impossible to achieve an exact adjustment of the relative speed between the movement of the tubing and the liquid transport, independent of the speeds at which the tubing and the liquid are conveyed.